1. Field of Invention
The invention relates to an ink jet apparatus, an ink jet apparatus driving method, and a storage medium for storing an ink jet apparatus control program.
2. Description of Related Art
In conventional ink jet apparatuses, the volumetric capacity of an ink channel is changed by deformation of piezoelectric ceramic. When the volumetric capacity is reduced, ink in the ink channel is ejected as an ink droplet from a nozzle and, when the volumetric capacity is increased, ink flows into the ink channel from an ink guide port. In a printhead for this kind of ink jet apparatus, a plurality of ink channels are formed and separated by piezoelectric ceramic sidewalls. An ink supplying means, such as an ink cartridge, is connected to one end of each ink channel, and an ink ejection nozzle (hereinafter referred to as a nozzle) is provided for the other end of each ink channel. Selective reductions of the volumetric capacity of the ink channels by deformation of the sidewalls, according to print data, cause ink droplets to be ejected from the corresponding nozzles onto a print medium and, as a result, characters and graphics are printed thereon.
Ink jet apparatuses of this kind, i.e., drop-on-demand type ink jet heads, which eject ink droplets for printing, are becoming widespread because of their excellent ejection efficiency and low running costs.
A problem with such conventional ink jet heads is that vibrations remaining in the ink channel after ink droplet ejection in response to a print command will affect ink droplet ejection in response to the next print command. As a result, the ink droplet trajectory may be curved or the ink droplet volume may be changed.
In recent years, the volume of an ink droplet to be ejected is variably adjusted to produce a gray-scale image. In this case, accurate ejection of a required volume of an ink droplet is critical to ensure high print quality. Printing at high speed, that is, dot forming at high frequencies, is susceptible to the residual vibrations in the ink channel and may result in changes in the ink droplet ejection volume and production of a poor gray-scale image.
Conventionally, adjustment of the ink droplet volume for printing a dot has been attempted by judging whether there is ink ejection immediately before a dot to be printed and by changing the voltage for ejecting ink to print the dot. However, because the residual vibrations vary depending on the previously ejected ink droplet volume, it has been difficult to adjust the ink droplet volume for printing a dot as required in a stable manner.
In view of the foregoing problems, the invention provides an ink jet apparatus and a driving method thereof that ensure stable ejection of a desired volume of an ink droplet for high-quality printing. A drive waveform for printing a dot is adjusted according to the presence or absence of an ejection pulse signal immediately before and/or after the dot to be printed and according to the waveform of each ejection pulse signal present immediately before and/or after the dot to be printed.
According to one aspect of the invention, a method of driving an ink jet apparatus is provided. The ink jet apparatus includes a nozzle from which an ink droplet is ejected, an ink channel filled with ink and connected to the nozzle, an actuator that changes a volumetric capacity of the ink channel to generate a pressure wave in the ink channel, and a controller that applies an ejection pulse signal to the actuator to cause ink droplet ejection from the nozzle. In the ink jet apparatus driving method, whether an ejection pulse signal is present at least immediately before or after a dot to be formed is judged and, if so, a drive waveform of the ejection pulse signal present at least immediately before or after the dot to be formed is judged. Then, based on results of the judgement, a drive waveform of an ejection pulse signal for forming the dot is adjusted.
In this method, a required volume of an ink droplet for forming a dot can be stably ejected, according to the condition of an ink meniscus in the nozzle and the residual vibrations in the ink channel, by judging whether there is ink ejection immediately before and/or after the dot to be formed and judging the drive waveform used for each ink ejection present immediately before and/or after the dot to be formed.
In this ink jet apparatus driving method, a plurality of drive waveforms are previously prepared as ejection pulse signals to be applied to the actuator and, the drive waveform for forming the dot is adjusted by selecting one of the plurality of drive waveforms, based on the results of the judgement. Accordingly, in this method, an optimum drive waveform for forming a dot can be selected according to the condition of an ink meniscus in the nozzle and the residual vibrations in the ink channel at the time of forming the dot.
Further, in this ink jet apparatus driving method, the ejection pulse signals are classified into groups by ink droplet ejection volume, and each group includes a plurality of ejection pulse signals having different drive waveforms. A drive waveform for forming a dot is adjusted by selecting an ejection pulse signal having a predetermined drive waveform from among a plurality of ejection pulse signals that are classified under a group designated for the dot to be formed.
In this method, an optimum drive waveform for forming a dot can be selected according to the condition of an ink meniscus in the nozzle and the residual vibrations in the ink channel and, as a result, a high-quality continuous gray-scale image can be produced.
According to another aspect of the invention, an ink jet apparatus to accomplish the above-described method is provided.
According to still another aspect of the invention, a storage medium for storing a program that accomplishes the above-described method is provided. The program in the storage medium is loaded into a personal computer, or the like, from which print data is outputted to an ink jet apparatus to perform printing.